The invention relates generally to electronic control systems for processing signals indicative of a motion condition and more particularly provides a hybrid analog digital controller for receiving an accelerometer input signal and producing an output signal indicative of absolute velocity. Specifically, the controller includes an analog integrator, digital feedback stabilizer and digital filter.
Active suspension systems accomplish motion attenuation by continuously controlling a suspension force independently of the relative movement of the suspension in real-time response to a command signal. Active systems are particularly useful when configured for control of motion between relatively moveable members such as in vehicular suspensions. Due to the relatively large power requirements typically required for generating appropriate suspension forces, systems of the so-called semi-active type have been proposed as exemplified in U.S. Pat. Nos. 3,807,678; 4,660,686; 4,468,050; and 4,468,739. The semi-active damper concept differs from fully active systems in that it does not employ an active actuator means, hydraulic pump or similar external source of high-pressure fluid to provide the damping force. It is the resistance to fluid flow within the system that generates the damper force. Thus, when the absolute velocity of the mass to be isolated is in a direction opposite to the relative motion between the mass and its support, the damper will not be able to provide a force in a direction to counteract the movement of the mass. In these instances, a zero or nonresistant force is produced by the system. The result is a most effective and energy efficient method of enhanced vibration control closely approximating the performance of fully active damping mechanisms.
Implementation of active suspension systems in, for example, vehicle suspension applications and for other complicated, high-order nonlinear systems having multiple degrees of freedom and a plurality of dampers requires system response to a variety of forces which may not be easily modulated or controlled. Input disturbances such as those caused by road surface irregularities, and inertial forces commonly associated with vehicle motion, must be continuously monitored for proper generation of counteracting suspension forces. An active damper ideally should generate compensating forces of appreciable magnitude only at times when the effect would be to attenuate the vibratory motion of the member that is to be isolated. Successful damper performance for any system is, therefore, greatly dependent upon the particular control algorithm employed to vary the damper forces. While an ideal result cannot be completely realized in practice, active suspension systems of the semi-active type can approach a high degree of vibration attenuation or isolation when the damper is operated in accordance with an appropriate control algorithm such as, for example, that disclosed in U.S. Pat. No. 3,807,678 and U.S. Pat. No. 4,491,207. These control algorithms produce damper forces in real-time response to a motion condition experienced by the system based upon a determination of the instantaneous absolute velocity of the sprung mass and upon a determination of the instantaneous relative velocity between the sprung mass and supporting mass interconnected by the damper assembly.
Instantaneous and continuous measurements of absolute velocity, while a common input parameter required for implementation of control algorithms of the above type, are difficult in practice to obtain for moving suspension systems. In order to realize such control algorithms, it is necessary to determine the absolute velocity of a point on a rigid body; i.e., a sprung mass or the frame of a vehicle. This value must be determined without the benefit of fixed reference. One approach to solving this problem is to obtain an estimate of absolute velocity or signal indicative of absolute velocity by integrating an accelerometer signal. The electronic hardware implementation required for generating an estimated absolute velocity signal is somewhat problematic and the results achieved heretofore have been less than ideal.
Complex digital systems can be designed that provide an accurate device or controller for generating a signal indicative of absolute velocity. For example, digital system implementation may utilize optimal control theory under a sophisticated theoretical foundation such as Kalman filtering. However, the use of digital filter design contemplates the performance of relatively complicated calculations that require detailed and cost prohibitive components to carry out the necessary functions. Likewise, digital systems usually will require an anti-aliasing filter to avoid sampling errors in the system. An anti-aliasing filter serves to attenuate high-frequency signal components which might provide erroneous information of overall system input.
Ideally, a controller constructed of analog components to perform signal integration is preferable due to low cost and simplicity of construction. Analog components further eliminate the need for expensive anti-aliasing filters due to their continuous nature. An analog controller would reduce the overall complexity of the system. However, it has been found that analog components such as capacitors and resistors in conjunction with operational amplifiers do not perform well under the frequency parameters common to the implementation of control algorithms for active devices. The operative band width for the controller is approximately between 0.5 and 20 hertz. In addition, corrupting noise is present with significant energy as high as 60 hertz. An analog integrating circuit will likely experience D.C. bias and large or infinite D.C. gain which will saturate the system components. Likewise, unusually large capacitors and resistors must be employed to overcome component inaccuracies. Leakage, large physical volumes and increased expense diminish the practical effectiveness of analog controller devices.
It is accordingly an object of the present invention to provide a controller for producing an output signal indicative of absolute velocity which eliminates or substantially minimizes the above mentioned and other problems and limitations typically associated with both digital and analog devices.